I started reading Attack on Titan about a year ago, when chapter 121 came out, I have been a big fan ever since. It is a truly unique story with interesting characters and compelling themes. All 138 chapters are very good, and are some of the best story telling I have seen. Just ignore the final chapter, skip it for the love of all that is holy. It is a complete assassination of everything you love and hold dear. Read fan theories instead, they are much better
I was told to write more for this review so I will continue *WARNING:SPOILERS*
Eren, Historia and Mikasa's characters and arcs are completely destroyed. Everyone's arc is, but these three have the most egregious writing sins committed against them. Eren ends up in one chapter being the most pathetic character in the series, committing horrific acts, and when questioned later on about it he says he can't remember why he did it just to name one major issue. Historia, you think she is going to be a very important character in the end, and may even have a romantic relationship with Eren, Isayama made their relationship important and made a lot of foreshadowing for nothing. She relegated to a background character. Mikasa is probably the worst, as her whole character past chapter 122 is just her obsessing over Eren. This is not a healthy relationship, and in the end she is miserable and would be better off dead.